1. Technical Field
The present invention relates to an optical information recording method for recording information on an optical information recording medium by driving and controlling an optical modulation waveform.
2. Background Art
The storage capacity of optical discs has been increasing, and Blu-Ray Discs (BDs) using blue laser (405 nm) have been marketed in addition to conventional CDs using infrared laser (wavelength of 780 nm) and DVDs using red laser (wavelength of 650 nm).
For example, a write strategy technology employed for DVD-RAMs uses multiple laser pulses having three different power levels as shown in FIG. 17. The three power levels are a write power (Pw), a gap power (Pg) and an erase power (Pe) in descending order of level. When a portion of an optical disc is irradiated with a laser beam of the write power Pw, a recording film in the portion of the optical disc melts. When being rapidly cooled thereafter, the portion of the optical disc becomes amorphous (noncrystalline) and the reflectance of light of the portion drops. This portion is used as a recording mark. When the optical disc is irradiated with a laser beam of the erase power Pe, the recording film of the optical disc becomes crystalline. Accordingly, the portion which has been amorphous before the laser irradiation becomes crystalline, while a portion which has been crystalline from the beginning remains crystalline. Thus, the recording mark can be erased.
The write strategy uses pulses such as a rectangular monopulse employed for CD-Rs, DVD-Rs and the like, a comb-like multipulse (see FIG. 17) employed for CD-RWs, DVD-RWs, DVD-RAMs and the like, a castle-type (non-multi type) pulse employed for high-speed recording of DVD-based optical discs.
A value for determining edge timing of a write waveform shown in FIG. 17 or FIG. 18, and values for determining recording powers such as Pw, Pg and Pe, are called write parameters. Optimal values of the write parameters are predetermined for and prerecorded in each recording medium. For example, in a DVD-RAM, the optimal values are recorded in a physical format information (PFI) area in a control data zone provided in a lead-in area along the inner circumference. This is because optimal values of a group of write parameters differ depending on the composition, the material and the like of each recording medium.
Specifically, to write a recording mark, write parameters are read from the recording medium, a laser pulse is controlled by using the write parameters thus read, and thereby an optimal recording mark is formed. Here, the write parameters read herein include a value for determining edge timing of a write waveform, values for determining recording powers such as Pw and Pg, and values in a shift table. Such a technique is disclosed in Japanese Patent Application Publication No. 2003-85753, for example.
If a recording mark is not formed properly in the recording, recorded data may not be reproduced correctly. For this reason, a recording mark needs to be formed properly. A method which has been employed to form a proper recording mark is to emit a pulsed laser beam and thereby control the heat build-up at the time of irradiating an optical disc recording film with the laser beam. In general, a semiconductor laser diode (referred to as a LD below) for emitting a laser beam is supplied with a pulsed current and thereby emits a pulsed laser beam.
A device which supplies a pulsed current to the LD is a laser driver (LDD). When the laser driver supplies a pulsed current to the LD, the LD emits light according to a light-emitting pattern based on pulse timing of the current supplied to the LD. Thus, the LD emits a pulsed laser beam, consequently forming a proper recording mark. In this description, a pulsed current which the laser driver supplies to the LD is referred to as a current pulse, and a waveform outputted from the LD is referred to as a light-emission pulse, below.
In recent years, the speed of recording data to an optical disc has been increasing every year. In nature, an influence of an electric circuit load between the LD and the laser driver exists to no small extent in the process of supplying a current pulse from the laser driver to the LD, and such an electric circuit load affects the current pulse supplied to the LD. As the width of the current pulse becomes smaller along with the increase of the recording speed, the influence of the electric circuit load between the LD and the laser driver exerted on the current pulse relatively increases, making it more difficult to supply a desired current pulse to the LD. If the desired current pulse is not supplied to the LD, the light emitted by the LD results in having a waveform different from a desired one. Accordingly, this influence appears significantly in a recording mark generated on a recording surface of the disc, and causes deterioration in recording quality. A resistance load of the LD is referred to as a differential resistance of the LD below (see FIG. 19).
As a solving means for the above-described problem, Japanese Patent Application Publication No. 2006-48885 describes a method which makes use of changes of an electrical circuit load between a LD and a laser driver according to temperature. In the method, information on the temperature at the time when the LD is in use or the load of the LD that changes according to the temperature is acquired, and thereby the laser driver generates an appropriate current pulse according to temperature. By supplying the LD with the appropriate current pulse that is generated according to the temperature, an appropriate laser beam can be emitted even if a change occurs in the temperature environment at the time when the LD is in use.